This invention relates to a processing method of oxides or ceramic system superconductive substances, and more particularly it relates to a method of processing said substances to wires so that they can readily be utilized in electric or electronic apparatuses.
While oxides or ceramic system superconductive substances come lately into the limelight in electronic industrial fields, scopes of their practical utilization shall rapidly be enlarged when inventions and development in them especially high temperature superconductive substances are further made. However, even if high temperature superconductive substances or materials of extremely high conductivity were invented or developed, their scopes of utilization will inevitably be limited unless they can be processed into desired configurations suited to purposes of their utilization, such as films, wires, tapes, and so on. Among these configurations, a wire shape would most extensively be utilized for many purposes such as for wires forming a coil, though it is difficult to have oxides or ceramic system superconductive materials processed to wire shapes, and though practical or industrially employable methods therefor have not been established. While it has been known to have superconductive substances drawn repeatedly so that they are formed into wires, it is extremely difficult by this conventional method to obtain wires which are uniform in dimensions and shapes, and do not have any broken portion. A proposal has been made, in which constituent powder raw materials of a superconductive substance are heated, melted, and poured into pipe-shaped sheathes so that the superconductive substance is shaped to a wire. Though this proposal can be carried out in a laboratory scale but can hardly be employed in a practically employable industrial scale. It is proposed also in Jin et al, Applied Physics Letters, 21 Sept. 87, Vol 51, No. 12, pp 943-45 that a Ag- or silver-coated metal wire is utilized as a metal core which serves initially to mechanically support an oxide powder and binder composite. Said Ag- or silver-coated metal wire makes a preform-wire with the oxide/binder composite thereof. This preform-wire is then melt processed by rapidly moving a torch flame and melting the outer portion of the oxide shell. This method is, however, very difficult not only to control a thickness of the oxide shell but also to obtain a smooth and uniform oxide shell, because the shell-making on the wire depends primarily upon the binder. It is nearly impossible to mechanically apply the oxide/binder powdery composite which is sticky, onto cylindrical surfaces of the wire in uniform dimension and shape, and without any pin hole therein. It is nearly impossible in this method also to heat only the thin outer portion of the slender Ba-Y-Cu-O shell without deforming and decomposing the Ag-wire which is also slender and the melting temperature of which is apparently lower than that of the Ba-Y-Cu-O shell. Should the Ag-wire and Ba-Y-Cu-O shell are thick enough to stand on the torch flame without being adversely affected as above-mentioned, they have to be drawn repeatedly after they have been subjected to the torch flame, whereby it becomes more difficult to obtain wires which are uniform in dimensions and shapes, and do not have any broken or pin-holed portion.